A technology proposed in the related art for measuring the position of a mobile terminal, calculates the differential in arrival times at multiple base stations of signals sent from a terminal, calculates the propagation distance of the signal from the node to each base station and then detected the node position. (Atsushi Ogino and 5 others, “Wireless LAN Integrated Access System (1) Evaluation of a position detection system”, 2003 Lecture-Publication archives, Institute of Electronics, Information and Communication Engineers IEICE, B-5-2003, p. 662)
Another technology of the related art proposes constructing a positioning system that utilizes a reference station, in order to synchronize the base stations. (Kenichi Mizugaki and 9 others, “3 nW/bps Super Low Power Consumption UWB Wireless Systems (6): Evaluation of 30 cm High Accuracy Positioning System”, 2005 Society Conference Lecture/Publication archives, Institute of Electronics, Information and Communication Engineers IEICE, A-5-15, p. 139.)
In a technology proposed in JP-A No. 14152/2002, a positioning system for making distance measurements by utilizing a spectrum spreading signal, creates a delay profile by subjecting the received RF wave to a matching filter process, and then makes use of this delay profile to measure the distance. Also, a technology proposed in JP-A No. 273778/2003, makes multiple delay profiles by performing matching filter processing on the delay profile of the received signal, and then utilizing those multiple delay profiles to measure the distance.
This invention is capable of improving positioning resolution by utilizing UWB-IR (Ultra wideband impulse radio) for wireless signals utilized in positioning systems and distance measuring systems.
FIG. 20 shows a typical waveform of a UWB-IR signal. The pulse width WTP is here defined as the amplitude in the period from 0 to 0. The measurement time accuracy can be improved, and a system with satisfactory positioning and distance measurement accuracy can be achieved by utilizing a narrow pulse width as shown in FIG. 20.
However, using this UWB-IR signal requires that the receiver capture a narrow width pulse and causing the problem of a larger hardware scale and higher power consumption. When receiving a pulse width WTP of approximately 2 ns for example, the sampling time period narrows as shown in FIG. 22, so that analog-to-digital (AD) converter is needed that operates at a speed of 500 MHz or higher, which is the multiplicative inverse of the WTP. Therefore, building a positioning or ranging system that utilizes UWB-IR signals by utilizing the technology in JP-A No. 14152/2002 or JP-A No. 273778/2003, causes the problems of high power consumption along with the increased hardware scale required to fabricate delay profiles.
The waveform received in multipath environments is not always for the direct path possessing the largest amplitude. FIG. 21 shows a typical receive waveform for a UWB-IR signal in a multipath environment. The vertical axis in the figure is the power component of the signal. Examining the FIG. 21 reveals that there are signals with higher power (amplitude) than the signal (first path) arriving earliest. The receiver in the above positioning systems and ranging systems must measure the first path output time. In normal data communication on the other hand, the signal received with the largest amplitude is the signal possessing the least communication errors yet signals with the most power have the problem of large positioning and distance measuring errors.
To resolve the above mentioned problems, the present invention provides a receiver, a receiver for a positioning and ranging system, and a positioning method for measuring the arrival time of a first path signal in the received signal with hardware having a simple structure and lower power consumption.
Typical aspects of this invention are described next. Namely, the receiver of this invention includes: a waveform measuring unit for performing multiple analog-to-digital conversions on the received signal while shifting the timing at each Δt at a frequency identical to the nominal pulse repetition frequency of a transmit signal made up of intermittent pulses subjected to direct spreading, or an integer multiple of the same frequency, and at a frequency lower than the multiplicative inverse of the pulse width, and storing the observation data from the receive signal in a storage area, and a first path estimator unit to estimate the arrival time of the first path arriving earliest time-wise in the receive signal, based on the stored observation data from the receive signal.
This invention provides a low-cost, low-power consumption receiver for positioning and ranging, capable of measuring the output time of the first arrival signal in a receive signal by low-speed signal processing.
The receiver of this invention performs analog-to-digital (A/D) conversion on a frequency identical to the nominal pulse repetition frequency or an integer multiple of that frequency, and at a frequency less than the multiplicative inverse of the pulse width; offsets the analog-to-digital conversion timing at each Δt and stores results from multiple receive signal measurements in a storage region, and estimates the earliest arrival time of the first path arriving time-wise in the receive signals, based on the stored waveform data from the receive signal.
The receiver then processes that data after analog-to-digital conversion by utilizing a matched filter whose tap coefficient matches the spreading code applied in the transmit signal, and sets the output with the highest S peak value among matched filter outputs within one cycle of measurement time as that output time.
The receiver next sets a specified threshold value from the stored waveform data and, waveform data with the earliest arrival time exceeding that threshold value is judged to be the first path signal.
The receiver next finds the time differential between the output time and the demodulated path time from the stored output time, and if there is a frequency deviation between the transmitter and receivers, finds the output time matching the respective waveform data from the time differential, and then estimates the frequency deviation between the transmitter and receiver, from the synchronizing tracking function for slaving the receiver clock to the receive signal, and then uses the frequency deviation results to correct the calculated output time.